The invention relates to the field of automotive electrical systems. Specifically, the invention is directed to a method of determining the moment following a start-up sequence for an IC engine as to when a starter/alternator should transition from start-up to generator function.
The trend in automotive electrical systems has always been towards more power and higher voltages. At this time, an element of the trend involves the combination of the alternator and starter into a single IC engine driven unit. This combined starter/alternator can be driven either directly on the crankshaft of the IC engine as a part of the flywheel, on one end, or the balancer, on the other. Alternatively, the starter/alternator can be mounted for gear, belt, or chain drive from the crankshaft along with other IC engine driven components (i.e., waterpump/A/C compressor/power steering pump, etc.)
The starter/alternator has become more powerful not only for increasing power (current and voltage) but also for more rapid and more fequent starting cycles of the IC engine as enhanced operating efficiencies are sought. In pursuit of these goals, the starter/alternator has become more sophisticated in its control systems and its responsiveness to system requirements for both starter functions and generating functions.
In older systems where the alternator and starter function were performed by separate devices, the need to determine the optimal moment to transition from a starter function to an alternator function did not exist. Rather, the vehicle operator, relying on vehicle familiarity and overall driving experience, actuated the starter until engine startup was perceived. To limit the possibility of damaging the starter from overspeed, a special one-way disengaging drive was sometimes employed.
The alternator or generator was connected into older systems by virtue of a regulator that either accepted charge into the system to meet an electrical load, or for battery charging, or kept the alternator out of the system altogether as necessary. The alternator or generator in older systems did not change function from a starter to an alternator or generator.
In more modern vehicles with combined starter/alternator devices, a need exists to transition the device from starter to alternator/generator function at an appropriate moment following IC engine start-up. If the transition occurs too quickly, the IC engine may not, in-fact, have started. If it occurs too slowly, damage to the starter/alternator device may occur either directly or to the driving/driven mechanical connection between the IC engine and the device. In either case, premature wear and/or replacement is the likely outcome.
The present invention is directed to determining and controlling the appropriate moment at which a belt or chain driven combined starter/alternator should transition from start-up mode to alternator/generator mode following an IC engine start-up sequence. The method relies on starter/alternator belt/chain tension or tensioner position to establish the timing of the transition.
In the tensioner position monitoring embodiment, the starter/alternator controller, or other monitoring controller, monitors the angular or linear position of the belt/chain tensioner for the drive belt/chain that includes the starter/alternator into the accessory drive system for the IC engine. The tensioner will rotate, or translate linearly, to a first position as the starter function is initiated and begins engine cranking. When the IC engine begins generating its own self-sustaining torque, the angular position, or linear position, of the tensioner will change accordingly in reaction to the change in drive being transferred to the IC engine. The starter/alternator controller will detect the change in position and then make the transition from starting mode to generation mode.
In the belt/chain tension monitoring embodiment, the belt/chain position is monitored for movement between a relatively slack and tensile condition. Following an initiation of IC engine cranking, the belt/chain position on the pull side of the starter/alternator pulley follows a straight line between the pulley tangent points of initial belt/chain contact. On the slack side of the starter/alternator pulley, the belt/chain is less straight and curves away from the line between the tangent points of contact at adjacent pulleys. When the IC engine begins to obtain self-sustaining operation, the slack side of the belt/chain is pulled straight as the IC engine accelerates. The monitoring controller will detect the change in belt/chain position and then signal the starter/alternator to make the transition from starting mode to generation mode.